A Novel Program Suspend Scheme for Improving the Reliability of 3D NAND Flash Memory

Abstract

Experimental results indicate that the conventional program suspend scheme in 3D NAND flash memory chip can generate unexpected additional read fail bits and reduce the reliability of 3D NAND flash memory. These extra read fail bits are observed when the program suspend command is issued during the program stage, and particularly, they become more obvious as the delay time between program suspend operation and other following operations exceeds tens of milliseconds. By analyzing the waveform of conventional program suspend scheme, it is suggested that the unexpected extra read fail bits are caused by the different occupancy of grain boundary traps (GBTs) in the polycrystalline silicon (poly-Si) channel during the idle time after the program suspend operation. Accordingly, a novel program suspend scheme is proposed by adding a “stabilizing” pulse immediately after the program stage. Silicon experimental data show that the proposed scheme can effectively limit the read fail bit count (FBC) to a normal range, thus improving the reliability of 3D NAND flash memory significantly.

Keywords

• 3D NAND flash memory
• program suspend operation
• fail bit count
• grain boundary trap